The invention relates to an orthodontic device with a base having a base surface for fixing the device to a tooth, and a slot for receiving an orthodontic archwire, which is defined by a bottom surface and two side surfaces arranged on either side of the bottom surface and aligned in substantially parallel spaced relation to each other, and extends in a straight line through the base in the longitudinal direction of the base on a side thereof facing away from the base surface, and with a cover element for at least partially covering the open side of the slot facing the bottom surface, wherein the side surfaces of the slot have a positively locking guide, which is aligned substantially parallel in relation to the longitudinal direction of the slot, and in which the cover element is slidably and detachably held on the base.
Such devices are used in orthodontics as special embodiments of so-called buccal tubes or brackets.
Buccal tubes are understood as being orthodontic attachment elements, which in the area of the lateral teeth serve to transmit the forces generated, for example, by archwires to the teeth. To this end, the buccal tubes are usually welded onto orthodontic bands, i.e., thin-walled metal rings, which are then pressed onto the crowns of the teeth and firmly cemented there. Alternatively, buccal tubes may also be adhesively bonded directly to the teeth.
Buccal tubes of this kind are also used on the so-called first molars, which, in youngsters at an age of usually less than twelve years, are understood as being the rearmost molars in the upper and lower jaws. The buccal tubes are used there for receiving an orthodontic archwire, which, as a rule, extends from the first molar on the left jaw side to the first molar on the right jaw side in the lower or upper jaw.
Brackets are understood as being orthodontic attachment elements, which are used from the incisors to and including the premolars in the upper and lower jaws and serve there to transmit the forces generated by archwires to the teeth. To this end, the brackets are usually secured to the teeth by means of an adhesive.
According to the conventional definition of buccal tubes and brackets, in the case of brackets the archwires are placed therein, whereas in the case of buccal tubes the archwires are slid in.
In order to intentionally move teeth during orthodontic treatment, archwires are inserted into the slots of brackets or into the openings of buccal tubes. If an archwire disposed in a bracket is twisted out of its position of rest by a misalignment of a tooth, it exerts by way of its elastic spring characteristics a force or a torque on the bracket or buccal tube and hence on the tooth. Whereas in the area of the brackets such archwires are inserted into slots provided therefor and held in the slot by means of thin wire ligatures or elastic plastic ligatures, there is no open slot in a buccal tube for receiving the archwire, but an opening, which may be in the form of a four-edged- or through-bore so that the orthodontist does not have to fix any ligatures to the buccal tube in the area of the molars, which is difficult to access.
If the orthodontic treatment includes the second molars, which in young patients usually break through later than the first molars, the buccal tubes are also attached to the second molars lying behind the first molars. In this case, it is advantageous for the orthodontist if the opening of the buccal tubes placed on the first molars is in the form of a slot.
Replacement of a buccal tube with a bracket usually requires removal of the cemented band to which the buccal tube is attached and reattachment of the bracket. This involves a great amount of work for the orthodontist and increases the risk of damaging the patient's tooth enamel. In order to avoid this, so-called convertible buccal tubes, which can be converted to a bracket by removing the wall of the through-bore on the buccal side, have already been used on the first molars.
In U.S. Pat. No. 3,838,514, a bracket is described, whose slot is covered on the buccal side by a cover element, which is fixed to the bracket by spot welds or braze points. Therefore, this bracket can also function as buccal tube.
Manufacture of brackets of such convertible design is relatively costly, as the bracket has to be joined to the cover element in a separate manufacturing step, for example, by welding or soldering. Moreover, with this joining technology, the amount of force for releasing the cover element from the bracket can only be inaccurately determined beforehand.
In U.S. Pat. No. 5,913,680, a bracket is described whose slot is closable by a small plate-shaped spring member. To this end, a side rim of the spring member engages a groove disposed in a side surface of the slot, while the side of the spring member opposite the side rim embraces wing members of the bracket.
In order that the spring member will be removable from the bracket with an acceptable amount of force, the spring member must be of correspondingly thin design, and the spring member, therefore, has sharp-edged rim areas, which increase the risk of injuring the wearer of the bracket.
A convertible buccal tube made of sintered metal and of integral design is known from U.S. Pat. No. 4,927,362. The buccal tube has a base for attachment to a tooth, and an elongated slot extends therethrough for reception of an archwire. The slot opening on the buccal side is covered by a cover plate which extends transversely over the cheek-facing side of the slot. The cover plate is integrally joined to the buccal tube adjacent the opposite side surfaces of the slot by elongated webs which extend along the entire length of the slot and have a smaller thickness than the cover plate. To open the slot, the cover plate has to be sheared from the buccal tube along both of the webs. The buccal tube may then be used as a normal bracket.
When severing the cover plate, undefined breakage locations and burrs remain on the buccal tube and may impede insertion of an archwire into the opened slot.
The object underlying the invention is, therefore, to create an orthodontic device of the kind mentioned at the outset, which is convertible, offers the wearer thereof an increased degree of security, and is easier to handle during the conversion without any special instruments.
This object is accomplished with an orthodontic device of the generic kind, in accordance with the invention, in that the positively locking guide is formed by two grooves disposed in side surfaces of the slot facing each other, and in that the cover element is of flat configuration at the side facing the bottom surface of the slot and has two guide elements, which are of complementary design to the grooves and engage the grooves in a positively locking manner.
The orthodontic device according to the invention offers the wearer thereof an increased degree of security and is easier to handle for the orthodontist in charge, as no undefined breakage locations and/or burrs are created when removing the cover element from the base, that might impede insertion of an archwire into the opened slot. The archwire is nevertheless securely held in the slot.
Therefore, the device according to the invention can be converted in a very simple way into a device with bracket function by the cover element being removed from the base in the longitudinal direction of the slot. The conversion may be reversed again by sliding the cover element in again. The converting procedure may be repeated virtually any number of times. This opens up new dimensions for the devices according to the invention by, for example, wingless brackets being made possible, with which the archwire in the slot of the bracket is held securely in the slot by a cover element instead of by ligatures anchored on wings.
Moreover, forces which must be applied when converting the device act substantially parallel to the base surface, so that the danger of inadvertently tearing the device off the tooth is minimized. Also, the devices according to the invention can be converted with precisely predeterminable forces, so that, again, the risk for the patient is reduced.
Furthermore, the device according to the invention is of two-piece design, and, therefore, its manufacture is more cost-effective, because injection molds with a simpler shape may be used.
The device according to the invention may be used both as buccal tube and as convertible buccal tube or as bracket on teeth other than molars, in which an archwire is ligatable by means of the cover element.
In accordance with the invention, the positively locking guide is formed by two grooves facing each other, which are disposed in side surfaces of the slot that face each other. The cover element has in the longitudinal direction two guide elements spaced from each other, which are of complementary design to the grooves and engage the grooves with positive locking. It is thereby ensured that the cover element is held on both sides of the slot and thus in a stable manner. In accordance with the invention, the cover element is of flat configuration at the side facing the bottom surface. It is thereby ensured that an archwire can come to rest against the bottom surface of the slot and against the cover element, so as to transfer the forces emanating from the archwire onto the base and from there onto the tooth to be treated. To ensure that the archwire can rest securely on the bottom surface and on the cover element, the cover element may have on the side facing the bottom surface of the slot a rib which projects into the slot.
If the device according to the invention is to be used as convertible buccal tube or as buccal tube, it is particularly advantageous for the grooves forming the positively locking guide to be aligned in parallel with the bottom surface of the slot, as an area of the bottom surface of the slot that is as large as possible can thus serve in a simple way as contact surface for the archwire to be inserted into the base.
The grooves forming the positively locking guide preferably extend at an acute angle to each other, so that the cover element can be wedged in the inserted position and, therefore, secured in this position.
Furthermore, the grooves may also be inclined at an acute angle to the bottom surface of the slot, so that upon inserting the cover element after placement of the archwire, the archwire can be secured with a clamped fit in the slot.
The slot is often of rectangular cross section transversely to its longitudinal direction, and the side surfaces defining the slot are usually of flat design. It is thereby ensured that the forces acting from a rectangular archwire are transmitted onto the base of the device and from there onto the tooth to be treated.
The cover element of the device according to the invention may be insertably and releasably held on the base, for example, by force locking, in particular, by friction locking. In accordance with an embodiment of the device according to the invention, which is preferred because it is easy to handle, the cover element in the completely inserted state is secured by a clamped or press fit in the positively locking guide on the base.
The cover element held on the base may be additionally provided with a receiver for a securing element, with which the cover element may be secured to the device in the fully inserted state. The cover element may be fixed, for example, by means of a wire or a ligature via the receiver to the base of the device.
Alternatively or additionally, the cover element may be provided with a locking element for securing the cover element to the base in the fully inserted state. Locking of the cover element to the base is achieved by, for example, a locking element engaging a cut-out provided on the base. To release the locking, the cover element may be provided with a recess into which the locking element is lowerable. Alternatively, the locking element may also be made of elastic material, so that upon removal of the cover element from the device, the locking element undergoes deformation and thus becomes disengaged.
In accordance with an advantageous embodiment of the device according to the invention, the cover element comprises a headpiece for gripping and removing the cover element. The headpiece may be arranged either at one end of the cover element or on the side of the cover element facing away from the slot so as to remove, for example, by hand, the cover element from the device or slidably insert the cover element by hand into the positively locking guide.
The headpiece may, for example, also be in the form of a hook or an eyelet. The cover element may thus be removed from the device or inserted into the slot of the base with, for example, a dental instrument.
It may be provided that one guide element or both guide elements of the cover element are interrupted in the longitudinal direction and do not extend over the entire length of the cover element. This has the advantage that when inserting the cover element, it can be guided more easily into the quite narrow space from the adjacent bracket as the cover element does not have to be inserted fully from the side owing to the interruption in the guide elements, but may first be inserted over approximately half of the length from the buccal side into the slot and subsequently slid sideways into the end position.
In order to keep the risk of injury to a wearer of the device according to the invention or even just irritations as low as possible, the cover element preferably has rounded edges on all sides thereof.
The cover element preferably has a veneer element for veneering the side of the base facing away from the base surface. The veneer element is preferably tooth-colored and can, therefore, conceal any aesthetically disadvantageous appearance of the base.
In a further preferred embodiment of the invention, it is provided that the cover element has at its front end in the direction of insertion a projection which in the inserted state protrudes out of the slot of the base.
This projection is preferably designed so as to be deformable, in particular thermoformable, in the inserted state.
Owing to the deformation of the projection, it can be designed as a mechanical securing element which, in addition to the force locking and positive locking between cover element and base prevents the cover element from becoming unintentionally detached from its fitting in the slot of the base. This may prove advantageous in a number of applications where the device is subjected to particular mechanical stress.
Alternatively, possibly after deformation, the projection may also be joined to the base of the device, for example, by laser welding, adhesive bonding, etc.
It is particularly simple when both the base and the cover element consist of metal, with, for example, spot welding by means of laser then resulting in a joint with a substance-to-substance bond between the cover element or its projection and the base.
When the cover element is to be removed from the slot again, this joint can then be simply released and the deformation of the projection reversed, so that the cover element can then be removed from the base without any difficulty.
In a variant, the deformation of the projection may be carried out by it being expanded in the area of a notch or a slot in the projection. The cover element is thereby prevented from being readily pulled out of the slot again. The expanded portion then forms a mechanical securing element here. The expanded portion may also be additionally joined to the base with a substance-to-substance bond by adhesive bonding, spot welding, etc., and, as mentioned hereinabove, this joint may, in turn, be simply released or broken, for example, with an instrument.
The device according to the invention may be configured both as bracket and as buccal tube.
To enable fixing of the device according to the invention to a tooth as simply as possible, the base surface of the base has a shape that is adapted to the corresponding tooth. To this end the base surface has a surface portion which is curved in one direction or in several directions.
The base of the device according to the invention may be made, for example, of metal, ceramics, plastic and/or reinforced plastic.
Like the base, the cover element may also be made of metal, ceramics, plastic and/or reinforced plastic, and, in view of aesthetic considerations, the material for the cover element may be selected independently of whatever material the base of the device is made from. It is particularly preferred for the cover element to be made of metal and/or plastic. In these cases, it is particularly easy to produce a mechanical securing element as described hereinabove. The following description of preferred embodiments of the invention serves in conjunction with the drawings to explain the invention in greater detail.